B lymphocytes respond to antigen by proliferating and differentiating into antibody-secreting plasmacytes. That response can be enhanced or inhibited by antigen-specific or idiotype-specific T helper (TH) and T supperssor (TS) cells, respectively. The TNP-specific IgA315-secreting MOPC-315 myeloma plasma cells arise by differentiation from malignant small, non-secretory lymphocytoid stem cells. That differentiation and proliferation can also be regulated by carrier-specific and idiotype-specific TH and TS cells. I propose to use the IgA315-specific and carrier-specific regulatory T cells which I characterized last year and the monoclonal MOPC-315 B cell subpopulations separated by counterflow centrifugal elutriation to determine those functional, surface membrane, and metabolic markers which are unique to each B cell differentiation stage and to determine how exposure to different regulatory stimuli (id315-specific TH vs. TS or carrier-induced TH for proliferation vs. carrier-induced TH for differentiation) alter their expression. This will characterize the B cell differentiation stages and will give insight into how such signals are translated intracellularly.